Fresnel lens

Fresnel lens ( / f r eɪ n ɛ l / fray- NEL gold / f r ɛ z n əl / FREZ -nəl ) is a kind of compact lens Originally developed by French physicist Augustin Jean Fresnel- for lighthouses . [1]

The design Allows the building of lenses of wide aperture and short focal length without the mass and volume of material That Would Be required by a lens of conventional design. A Fresnel lens can be made much thinner than a comparable flat lens, in some cases taking the form of a flat sheet. A Fresnel lens can capture more oblique light from a light source, thus allowing the light from a lighthouse to be visible over greater distances.

History

The idea of ​​creating a thinner, lighter lens in the form of a series of annular steps is often attributed to Georges-Louis Leclerc, Count of Buffon . [2] Proposed Buffon, proposed by the Marquis of Condorcet (1743-1794), proposing a single piece of glass . [3] French physicist and engineer Augustin-Jean Fresnel is most often given credit for the development of the multi-part lens for use in lighthouses. According to Smithsonian magazine, the first Fresnel lens was used in 1823 in the Cordouan lighthouse at the mouth of the Gironde estuary; it’s 20 miles (32 km) out. [4] Scottish physicist Sir David Brewster is credited with convincing the United Kingdom to adopt these lenses in their lighthouses. [5] [6]

Description

1: Cross section of a spherical Fresnel lens
2: Cross section of a standard spherical plano-convex lens of equivalent power

The Fresnel lens reduces the amount of material required compared to a standard set of concentric annular sections. An ideal Fresnel lens would have infinitely many such sections. In each section, the overall thickness is compared to an equivalent single lens. This effectively provides a continuous surface of a standard set of surfaces of the same curvature, with stepwise discontinuities between them.

In some lenses, the curved surfaces are replaced with flat surfaces, with a different angle in each section. Such a lens can be seen in an array of prisms arranged in a circular fashion, with steeper prisms on the edges, and a flat gold slightly convex center. In the first (and largest) Fresnel lenses, each section was actually a separate prism. ‘Single-piece’ Fresnel lenses were later produced, being used for automobile headlamps, brake, parking, and turn signal lenses, and so on. In modern times, computer-controlled milling equipment (CNC) might be used to manufacture more complex lenses.

Fresnel lens design allows a substantial reduction in thickness, and at the expense of reducing the size of the lens.

Fresnel lenses are usually made of glass or plastic; their size varies from large (old historical lighthouses, meter size) to medium (book-reading aids, OHP viewgraph projectors) to small ( LRT / SLR camera screens, micro-optics). In many cases they are very thin and flat, almost flexible, with thicknesses in the 1 to 5 mm (0.039 to 0.197 in) range.

Modern Fresnel lenses usually consist of all refractive elements. However, many of the lighthouses have both refracting and reflecting elements, as shown in the photographs and diagrams. That is, the outer elements are sections of reflectors while the inner elements are sections of refractive lenses. Total internal reflectionwas often used to avoid the light loss of a silvered mirror.

Lighthouse lens sizes

Fresnel produced six sizes of lighthouse lenses, divided into four orders based on their size and focal length. [7] In modern use, these are classified as first through sixth order. An intermediate size between third and fourth order is added later, and

A first-order lens has a focal length of 920 mm (36 in) and a maximum diameter of 2590 mm (8.5 ft) high. The complete assembly is 3.7 m (12 ft) tall and 1.8 m (6 ft) wide. The smallest (sixth-order) has a focal length of 150 mm (5.9 in) and an optical diameter of 433 mm (17 in) high. [7] [8] [9]

The largest Fresnel lenses are called hyperradiant Fresnel lenses . One Such Was on hand lens When It Was Decided to build and outfit the Makapuu Point Light in Hawaii. Rather than order a new lens, the huge optic construction, 3.7 meters (12 ft) tall and with over a thousand prisms, was used there. [10]

Lighthouse lens orders
[ hide ]Order Focal length
(mm)
Height
(m)
First installed
Eighth
Seventh
Sixth 150 0433
Fifth 182.5 0541
Fourth 250 0722
3 1/2 375
Third 500 1576
Second 750 2069
First 920 2.59
Mesoradial 1125
Hyperradial 1330 1879
  • First-order lens

  • A first-order lens on the left

  • Close-up of a second-order lens

  • Third-order lens (Sekizaki Lighthouse, Oita, Japan)

  • Third-order lens at St. Simons Island Light

  • Fourth-order lens ( Nobska Light )

Types

There are two main types of Fresnel lens: imaging and non-imaging . Imaging Fresnel lenses use segments with curved cross-sections and produce sharp images, while non-imaging lenses have segments with flat cross-sections, and do not produce sharp images. [11] As the number of segments increases, the two types of lens become more similar to each other. In the abstract case of an infinite number of segments, the difference between curved and flat segments disappears.

Imaging

Spherical
A spherical Fresnel lens is equivalent to a simple spherical lens , using ring-shaped segments that are each a portion of a sphere, which all focus light on a single point. This type of lens produces a sharp, diffractive image at the edges of the ridges.
Cylindrical
A cylindrical Fresnel lens is equivalent to a single cylindrical lens , using straight segments with circular cross-section, focusing light on a single line. This type produces a sharp image, is not quite as clear as the simple cylindrical lens due to diffraction at the edges of the ridges.

Non-imaging

Spot
A non-imaging spot Fresnel lens uses ring-shaped segments with cross sections that are straight lines rather than circular arcs. Such a lens can focus on a small spot, but does not produce a sharp image. These lenses have application in solar power, such as sunlight on a solar panel. Fresnel lenses may be used as a basis for Köhler illumination optics resulting in very effective nonimaging optics Fresnel-Köhler (FK) solar concentrators. [12]
Linear
A non-linear imaging Fresnel lens uses straight segments whose cross sections are straight lines rather than arcs. These lenses focus light into a narrow band. They do not produce a sharp image, but can be used in solar power, such as to focus sunlight on a pipe, to heat the water within: [1] .

Uses

Imaging

A plastic Fresnel lens sold as a TV-screen enlarging device

The Fresnel lens used in the Sinclair FTV1 portable CRT TV, which enlarges the vertical aspect of the display only

Fresnel lenses are used as simple hand-held magnifiers . They are also used to correct several visual disorders, including ocular-motility disorders such as strabismus . Fresnel lenses have been used to increase the size of CRT displays in pocket televisions , notably the Sinclair TV80 . They are also used in traffic lights .

Fresnel lenses are used in left-hand-drive European lorries Reviews entering the UK and Republic of Ireland (and vice versa, right-hand-drive Irish and British trucks Reviews entering mainland Europe) to Overcome the blind spots Caused by the driver operating the lorry while sitting on the wrong side of the cab on the side of the road the car is on. They attach to the passenger-side window. [13]

Another automobile application of a Fresnel lens is a rear view enhancer, the view of the lens of a lens attached to the rear view of a vehicle, particularly a tall or bluff-tailed one, more effectively than a rear-view mirror alone.

Multi-focal Fresnel lenses are also used as a part of retina identification cameras, where they provide multiple in- and out-of-focus images of a fixation target inside the camera. For virtually all users, at least one of the images will be in focus, thus allowing correct eye alignment.

Fresnel lenses have also been used in the field of popular entertainment. The British rock artist Peter Gabriel made use of them in his early solo performance to magnify the size of his head, in contrast to the rest of his body, for dramatic and comic effect. In the Terry Gilliam film Brazil , plastic Fresnel screens appear ostensibly as magnifiers for the small CRT monitors used in the offices of the Ministry of Information. However, they occasionally appear between the actors and the camera, distorting the scale and composition of the scene to humorous effect. The Pixar movie Wall-E features a fresnel lens in the scenes where the protagonist watches the musical magnified on an iPod.

Photography

Canon and Nikon have used Fresnel lenses to reduce the size of telephoto lenses. Photographic lenses that include Fresnel elements can be much shorter than conventional lens design. Nikon calls their technology Phase Fresnel . [14] [15]

The Polaroid SX-70 camera used in Fresnel reflector as part of its viewing system.

View and large format cameras can be used in a Fresnel lens in conjunction with the ground glass , to increase the perceived brightness of the image projected by a lens on the ground glass, thus aiding in adjusting focus and composition.

Illumination

Inchkeith lighthouse lens and drive mechanism

High-quality glass Fresnel lenses have been used in lighthouses, where they were considered state of the art in the late 19th and 20th centuries; most are now retired from service. [16] Lighthouse Fresnel lens systems Typically include extra annular prismatic Elements, arrayed in faceted domes Above and below the central planar Fresnel, in order to catch all Emitted light from the light source. The light path through these elements can include an internal reflection , rather than the simple refractionin the plane Fresnel element. These lenses are very useful for the designers, builders, and users of lighting and their illumination. Among other things, smaller lenses could fit into more compact spaces. Greater light transmission over longer distances, and varied patterns, made it possible to triangulate a position. [17]

Perhaps The Most Widespread use of Fresnel lenses, for a time, occurred in automotive headlamps , Where They can shape the Roughly parallel beam from the parabolic reflector to meet requirements for dipped and main-beam patterns, Often Both in the Sami headlamp unit (Such as the European H4 design). For reasons of cost, weight, and impact resistance, newer cars have dispensed with glass Fresnel lenses, using multifaceted reflectors with plain polycarbonate lenses. However, Fresnel lenses continue in automotive tail, marker, and backup lights.

Glass Fresnel lenses are also used in lighting instruments for theater and motion pictures (see Fresnel lantern ); such instruments are often called Fresnels . The whole instrument consists of a metal housing, a reflector, a lamp assembly, and a Fresnel lens. Many Fresnel instruments allow the lamp to be moved to the lens of the focal point , to increase or decrease the size of the light beam. As a result, they are very flexible, and can often produce a beam as narrow as 7 ° or as wide as 70 °. [18] The Fresnel lens produces a very soft-edged beam, so is often used as a wash light. A holder in front of the lens can hold a colored plastic film ( gelto tint the light or wire screens or frosted plastic to diffuse it. The Fresnel lens is useful in the making of motion pictures because its ability to focus on the beam of a typical lens, but also because the light is relatively consistent across the entire beam of light.

Optical Landing System USS Navy aircraft carrier USS Dwight D. Eisenhower

Aircraft carriers and naval air stations typically use Fresnel lenses in their optical landing systems . The meatball light aids the proper glide slope for the landing. In the center are amber and red lights. Although the lights are always on, the angle of the lens of the pilot’s point of view and the position of the visible light. If the lights appear above the horizontal bar, the pilot is too high. If it is below, the pilot is too low, and if the lights are red, the pilot is very low.

The Fresnel lens has seen the light of day.

Projection

The use of Fresnel lenses for image projection reduces image quality, so they are likely to be prohibitively expensive. Cheap Fresnel lenses can be stamped or transparent and are used in overhead projectors and projection televisions .

Fresnel lenses of different focal lengths (one collimator , and one collector) are used in commercial and DIY projection. The collimator lens has the lower focal length and is placed closer to the light source, and the collector lens, which focuses on the light in the triplet lens, is placed after the image projection (an active LCD matrix panel in LCD projectors ). Fresnel lenses are also used as collimators in overhead projectors .

Solar power

Since plastic Fresnel lenses can be made larger than glass lenses, as well as being white Cheaper and much lighter, They Are used to concentrate sunlight for heating in solar cookers , solar in forges and in solar collectors used to heat water for domestic use. They can also be used to generate Stirling Engine .

Fresnel lenses can concentrate sunlight onto solar cells with a ratio of almost 500: 1. [19] This allows the active solar-cell surface to be reduced, lowering cost and allowing the use of more efficient cells that would otherwise be too expensive. [20] In the early 21st century, Fresnel reflectors began to be used in concentrating solar power (CSP) plants to concentrate solar energy. One app Was to preheat water at the coal-fired Liddell Power Station , Hunter Valley in Australia.

Fresnel lenses can be used to sinter sand, allowing 3D printing in glass. [21]

In fiction

The English children’s fantasy television series Shadows features an episode “The Other Window”, in which a scientist places a Fresnel lens on a window of his home, and his children and visions of their ancestors in previous centuries in it .

See also

  • Fresnel imager
  • Fresnel flat area
  • Lenticular lens
  • Linear Fresnel reflector
  • Prism lighting – Fresnel anidolic optics

References

  1. Jump up^ “Fresnel lens” . Merriam-Webster . Archived from the original on 17 December 2013 . Retrieved 19 March 2013 .
  2. Jump up^ “Fresnel lens” . Encyclopædia Britannica . Encyclopædia Britannica Online. Encyclopædia Britannica Inc. 2012 . Retrieved 5 July 2012 .
  3. Jump up^ “Fresnel lens” . Appleton’s dictionary of machines, mechanics, engine-work, and engineering . New York: D. Appleton and Co. 2 : 609. 1874 . Retrieved 5 July 2012 .
  4. Jump up^ Watson, Bruce. “Science Makes a Better Lighthouse Lens.” Smithsonian. August 1999 v30 i5 p30. produced inBiography Resource Center. Farmington Hills, Mich .: Thomson Gale. 2005.
  5. Jump up^ “Brewster, Sir David.” Encyclopædia Britannica. 2005. Encyclopædia Britannica Online. November 11, 2005.
  6. Jump up^ “David Brewster.” World of Invention, 2nd ed. Gale Group, 1999.
  7. ^ Jump up to:b Mabel A. Baiges (1988). Fresnel Orders (TIFF) . Archived from the original on 21 September 2015 . Retrieved 9 September 2012 .
  8. Jump up^ “Fresnel lenses” . Archived from the original on 27 September 2007. Retrieved 1 June 2007 .
  9. Jump up^ “Fresnel lenses” . Michigan Lighthouse Conservancy. 31 January 2008. Archived from the original on 21 September 2012 . Retrieved 9 September 2012 .
  10. Jump up^ “Makapu`u, HI” . Anderson, Kraig. Lighthouse Friends. Archivedfrom the original on 5 October 2008 . Retrieved 26 February 2009 .
  11. Jump up^ Nonimaging Opticsby R. Winston, JC Miñano, and PG Benítez, (Academic, 2005).
  12. Jump up^ Chaves, Julio (2015). Introduction to Nonimaging Optics, Second Edition . CRC Press . ISBN  978-1482206739 . Archived from the original on 18 February 2016.
  13. Jump up^ Lowe, David (3 December 2011). Lowe’s Transport Manager and Operator’s Handbook 2012 . Kogan Page Publishers . ISBN  9780749464103 . Archived from the original on 15 February 2017.
  14. Jump up^ Nikon Archived15 February 2015 at theWayback Machine.
  15. Jump up^ Digital Picture Archived14 January 2015 at theWayback Machine.
  16. Jump up^ Terry Pepper, Seeing the Light, The Incredible Fresnel Lens.Archived29 May 2008 at theWayback Machine.
  17. Jump up^ Terry Pepper, Seeing the Light, Fresnel lens. Archived29 May 2008 at theWayback Machine.
  18. Jump up^ Mum, Robert C.,Photometrics Handbook. Broadway Press. 2nd Edition. Page 36.
  19. Jump up^ “Soitec’s Concentrix technology” . Archived from the original on 17 April 2011 . Retrieved 3 September 2013 .
  20. Jump up^ “Soitec’s High-Performance Concentrix Technology” . Archived fromthe original on 23 September 2013 . Retrieved 3 September 2013 .
  21. Jump up^ “Archived copy” . Archived from the original on 8 May 2017 . Retrieved 18 May 2017 .

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